Feedback Based on Codebook Subset

ABSTRACT

The present invention provides for an improved application of signal strength weightings in a SDMA sectorized cellular network. The improved signal strength weightings application is conducted through the improved selection of weightings from a new codebook subset or by the selection of weightings from a larger codebook subset. In a further embodiment, an antenna beam index or bit map can be used to select the best beam(s) in a SDMA sectorized cellular network. In another embodiment, a field or factor in an uplink or downlink transmission packet can designate which directional transmission beam is best suited for the transmission or when the directional transmission beam should be activated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of

-   -   U.S. patent application Ser. No. 16/357,425, filed Mar. 19,        2019, titled “Feedback Based on Codebook Subset”, by Lai King        Tee, Yi Song and Neng Wang, which is a continuation of    -   U.S. patent application Ser. No. 16/110,853, filed Aug. 23,        2018, titled “Feedback Based on Codebook Subset”, by Lai King        Tee, Yi Song and Neng Wang, now U.S. Pat. No. 10,277,294, which        is a continuation of    -   U.S. patent application Ser. No. 15/894,154, filed Feb. 12,        2018, titled “Feedback Based on Codebook Subset”, by Lai King        Tee, Yi Song and Neng Wang, now U.S. Pat. No. 10,063,298, which        is a continuation of    -   U.S. patent application Ser. No. 15/331,979, filed Oct. 24,        2016, titled “Feedback Based on Codebook Subset”, by Lai King        Tee, Yi Song and Neng Wang, now U.S. Pat. No. 9,923,616, which        is a continuation of    -   U.S. patent application Ser. No. 14/997,871, filed Jan. 18,        2016, titled “Feedback Based on Designated Subset of Codebook”,        by Lai King Tee, Yi Song and Neng Wang, now U.S. Pat. No.        9,479,239, which is a continuation of    -   U.S. patent application Ser. No. 14/561,285, filed Dec. 5, 2014,        titled “Codebook Subset Selection”, by Lai King Tee, Yi Song and        Neng Wang, now U.S. Pat. No. 9,270,351, which is a continuation        of    -   U.S. patent application Ser. No. 14/146,764, filed Jan. 3, 2014,        titled “Codebook Subset Selection”, by Lai King Tee, Yi Song and        Neng Wang, now U.S. Pat. No. 8,909,156, which is a continuation        of    -   U.S. patent application Ser. No. 13/758,446, filed Feb. 4, 2013,        titled “Weighting Matrix Selection Based on Information Acquired        from Remote Station”, by Lai King Tee, Yi Song and Neng Wang,        now U.S. Pat. No. 8,644,764, which is a continuation of    -   U.S. patent application Ser. No. 12/989,749, filed Oct. 26,        2010, titled “Performance for a Multiple Antenna Beamforming        Cellular Network”, by Lai King Tee, Yi Song and Neng Wang, now        U.S. Pat. No. 8,391,797, which is    -   the U.S. National Stage of International Application No.        PCT/US09/02585, filed Apr. 28, 2009, which claims the benefit of        priority to    -   U.S. Provisional Application No. 61/048,716, filed on Apr. 29,        2008.

All of the above-identified applications are hereby incorporated byreference in their entireties as though fully and completely set forthherein.

The claims in the instant application are different than those of theparent application or other related applications. The Applicanttherefore rescinds any disclaimer of claim scope made in the parentapplication or any predecessor application in relation to the instantapplication. The Examiner is therefore advised that any such previousdisclaimer and the cited references that it was made to avoid, may needto be revisited. Further, any disclaimer made in the instant applicationshould not be read into or against the parent application or otherrelated applications.

FIELD OF THE INVENTION

A system and method for selection of codebook subset in a mobilecommunication system having multiple transmit antennas.

BACKGROUND OF THE INVENTION

There is an increasing demand on mobile wireless operators to providevoice and high-speed data services, and at the same time, theseoperators want to support more users per base station to reduce overallnetwork costs and make the services affordable to subscribers. As aresult, wireless systems that enable higher data rates and highercapacities are needed. The available spectrum for wireless services islimited, and the prior attempts to increase traffic within a fixedbandwidth have increased interference in the system and degraded signalquality.

One problem exists when prior art omni-directional antennas are used atthe base station because the transmission/reception of each user'ssignal becomes a source of interference to other users located in thesame cell location on the network, making the overall systeminterference limited. Such an omni-directional antenna is shown in FIG.1(a). In these traditional mobile cellular network systems, the basestation has no information on the position of the mobile units withinthe cell and radiates the signal in all directions within the cell inorder to provide radio coverage. This results in wasting power ontransmissions when there are no mobile units to reach, in addition tocausing interference for adjacent cells using the same frequency, socalled co-channel cells. Likewise, in reception, the antenna receivessignals coming from all directions including noise and interference.

An effective way to reduce this type of interference is to use multipleinput-multiple output (MIMO) technology that supports multiple antennasat the transmitter and receiver. For a multiple antenna broadcastchannel, such as the downlink on a cellular network, transmit/receivestrategies have been developed to maximize the downlink throughput bysplitting up the cell into multiple sectors and using sectorizedantennas to simultaneously communicate with multiple users. Suchsectorized antenna technology offers a significantly improved solutionto reduce interference levels and improve the system capacity.

The sectorized antenna system is characterized by a centralizedtransmitter (cell site/tower) that simultaneously communicates withmultiple receivers (user equipment, cell phone, etc.) that are involvedin the communication session. With this technology, each user's signalis transmitted and received by the base station only in the direction ofthat particular user. This allows the system to significantly reduce theoverall interference in the system. A sectorized antenna system, asshown in FIG. 1(b), consists of an array of antennas that directdifferent transmission/reception beams toward each user in the system ordifferent directions in the cellular network based on the user'slocation.

The radiation pattern of the base station, both in transmission andreception, is adapted to each user to obtain highest gain in thedirection of that user. By using sectorized antenna technology and byleveraging the spatial location of mobile units within the cell,communication techniques called space-division multiple access (SDMA)have been developed for enhancing performance. Space-Division MultipleAccess (SDMA) techniques essentially creates multiple, uncorrelatedspatial pipes transmitting simultaneously through beamforming and/orprecoding, by which it is able to offer superior performance in multipleaccess radio communication systems.

This method of orthogonally directing transmissions and reception ofsignals is called beamforming, and it is made possible through advancedsignal processing at the base station. In beamforming, each user'ssignal is multiplied with complex weights that adjust the magnitude andphase of the signal to and from each antenna. This causes the outputfrom the array of sectorized antennas to form a transmit/receive beam inthe desired direction and minimizes the output in other directions,which can be seen graphically in FIG. 2.

While known methods exist in the conventional multi-user multipleantenna systems that employ an orthogonal precoder to place weightingson the spatially orthogonal beamforming transmissions, the known methodsand systems are not optimized in the precoding operations, and therebyfail to optimize the performance on the network. The present inventionresolves these problems. Further, the installation of many antennas atsingle base stations can have many challenges which are resolved by thepresent invention. Since the available spectrum band will probably belimited while the requirement of data rate will continuously increase,the present invention also supports an expansion of the availablespectrum over known methods for precoding in the cellular network.

The various components on the system may be called different namesdepending on the nomenclature used on any particular networkconfiguration or communication system. For instance, “user equipment”encompasses PC's on a cabled network, as well as other types ofequipment coupled by wireless connectivity directly to the cellularnetwork as can be experienced by various makes and models of mobileterminals (“cell phones”) having various features and functionality,such as Internet access, e-mail, messaging services, and the like.

Further, the words “receiver” and “transmitter” may be referred to as“access point” (AP), “base station,” and “user” depending on whichdirection the communication is being transmitted and received. Forexample, an access point AP or a base station (eNodeB or eNB) is thetransmitter and a user is the receiver for downlink environments,whereas an access point AP or a base station (eNodeB or eNB) is thereceiver and a user is the transmitter for uplink environments. Theseterms (such as transmitter or receiver) are not meant to berestrictively defined, but could include various mobile communicationunits or transmission devices located on the network.

SUMMARY OF THE INVENTION

The present invention provides for an improved application of signalstrength weightings in a SDMA sectorized cellular network. The improvedsignal strength weightings application is conducted through the improvedselection of weightings from a new codebook subset or by the selectionof weightings from a larger codebook subset. In a further embodiment, anantenna beam index or bit map can be used to select the best beam(s) ina SDMA sectorized cellular network. In another embodiment, a field orfactor in an uplink or downlink transmission packet can designate whichdirectional transmission beam is best suited for the transmission orwhen the directional transmission beam should be activated.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention will become more readilyunderstood from the following detailed description and appended claimswhen read in conjunction with the accompanying drawings in which likenumerals represent like elements and in which:

FIG. 1 is a graphical illustration of an omni-directional antenna (a)and a sectorized antenna (b);

FIG. 2 is a graphical illustration of a weighted sectorized transmissionbeam directed to the desired user;

FIG. 3 is a graphical illustration of a multiple antenna transmissionsystem using precoding;

FIG. 4 is a codebook subset table for constant modulus;

FIG. 5 is a codebook subset table for antenna selection;

FIG. 6 is a precoding codebook subset table;

FIG. 7 is a precoding codebook subset table;

FIG. 8 is a precoding codebook subset table proposed in the presentinvention;

FIG. 9 is a precoding codebook subset table proposed in the presentinvention;

FIG. 10 is a larger precoding codebook subset table proposed in thepresent invention; and,

FIG. 11 is a precoding codebook subset table proposed in the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1(a), the overall transmission architecture 100 of anomni-directional antenna 105 that transmits radially outward equally invarious directions shown by arrows 125, 115, 135 and 140. The perimeterof the coverage area is shown by the area 120 for the transmissionarchitecture 100. Improved efficiencies have been achieved by using thesectorized antenna architecture 140 shown in FIG. 1(b).

Multiple antennas 145, 147 and 148 are shown in the architecture 140,wherein each antenna is directed toward a different region of thecellular network shown by the directional transmission 175 for coveragearea 150, transmission 190 for coverage area 157, and directionaltransmission 180 for coverage area 155. In this context, it is possiblefor system capacity to be improved by the sectorized architecture.

By weighting the various transmission signals, additional efficienciesand reduced interferences can be achieved as shown in FIG. 2 for thesectorized architecture 200. Multiple antenna elements 215, 220, 227 and230 direct transmissions (or receive transmissions) in the sectorizedantenna architecture 200. A directional antenna beam 235 is formed byscaling the signal with a set of weighting factors applied to an arrayof antenna elements, such as antenna element 230. The desired user 205is shown receiving a desired transmission 245 in the coverage area ofthe directional antenna beam 235, which is a heavily weightedtransmission meant to be directed to that user 205. An interfering user210 is shown with less weighted transmission signals 240 to reduce theinterference encountered by that user 210.

In FIG. 3, a precoding architecture 300 is shown where a data input 301is fed into the user selection component 310. The user selectioncomponent 310 sends the appropriate data through the appropriate datasignal line 315 to the precoding component 321. The appropriate data foreach user 350, 351, 352 may consist of channel encoded, interleaved,rate-matched, scrambled and/or modulated symbols. The precodingcomponent 321 provides an appropriate weighting for the signal strengthto be transmitted on the multiple antennas 320, 322 or 325. Based on thetargeted user 350, 351 and 352, the signal strength weighting of themultiple antennas to each of these targeted user will be adjusted toincrease the efficiency of the data transfer to the desired user andreduce interference with other users on the system.

The selection of specific codes to be used in the precoding component321 to provide appropriate weightings for the signal strength are shownin several tables documented in FIGS. 4-11. In FIG. 4, a constantmodulus 2-Tx codebook is shown, and in FIG. 5, an antenna selection 2-Txcodebook is shown. A codebook accepted under the TS 36.211 v8.2.0standard is shown in FIG. 6.

There are two possible configurations for the codebook selection usingthe codebooks at FIGS. 4, 5 and 6. In one configuration, the attachmentpoint (base station/antenna) may select one of the two subsets shown inFIG. 4 or 5 for use in a sector where the user is located. Theattachment point selects a subset codebook for all user equipment in thesame sector, such as using only the codebook shown in FIG. 4 or 5. Theattachment point selects the codebook subset for the user equipmentbased on some knowledge of the user equipment's channel condition. Thechannel condition information includes information regarding the userequipment's location information, the error rate for transmissions tothe user equipment, the number of re-transmissions to the userequipment, and the uplink sounding or other uplink transmissions, withthe uplink received beam-forming using a similar beam pattern as thatfor the downlink transmission.

In a second configuration, the user equipment can select the appropriatecodebook subset to be used in FIGS. 6, and the user equipment can selectbetween a total of 9 different distinct codewords for a 2-Tx twotransmission antenna system. The user equipment transmits an indicatorthat implicitly or explicitly indicates which codebook subset is chosen.The subset selection will be dictated in the second configurationthrough a higher layer activation depending on the codeword selectedfrom the codewords shown in FIG. 6, and the index of the selectedcodeword in the subset is signaled using 2 bits through the normal PMIfeedback indicator field value. To support this approach, the PMIindicator for both the downlink and uplink signaling needs 2-bits.

As an alternative, the codebook shown in FIG. 7 can be substituted forthe various codebooks shown above in FIG. 4 or 5. Instead of using thepreviously-identified codebooks in FIGS. 4-7, the present invention alsosupports the use of codebook subsets shown in FIGS. 8 and 9, either ofwhich can be used in the above configurations. That is, the codebooks inFIGS. 8 and 9 can be selected using two configurations.

In one configuration, the attachment point (base station/antenna) mayselect one of the two subsets shown in FIG. 7, and either FIG. 8 or 9for use in a sector where the user is located. The attachment pointselects a subset codebook for all user equipment in the same sector,such as using only the codebook shown in either FIG. 8 or 9. Theattachment point selects the codebook subset for the user equipmentbased on some knowledge of the user equipment's channel condition. Thechannel condition information includes information regarding the userequipment's location information, the error rate for transmissions tothe user equipment, the number of re-transmissions to the userequipment, and the uplink sounding or other uplink transmissions, withthe uplink received beam-forming using a similar beam pattern as thatfor the downlink transmission.

In a second configuration, the user equipment can select the appropriatecodebook subset to be used in either FIG. 8 or 9, and the user equipmentcan select between the different distinct codewords for a twotransmission antenna (2-Tx) system. The user equipment transmits anindicator that implicitly or explicitly indicates which codebook subsetis chosen. The subset selection will be dictated in the secondconfiguration through a higher layer activation depending on thecodeword selected from the codewords shown in FIG. 7, and either FIG. 8or 9, and the index of the selected codeword in the subset is signaledusing 2 bits through the normal PMI feedback indicator field value. Tosupport this approach, the PMI indicator for both the downlink anduplink signaling needs 2-bits.

Further, the attachment point may also use a larger codebook subsettable as shown in FIGS. 10 and 11 for use in a sector where the user islocated. The attachment point selects a codebook for all user equipmentin the same sector, such as using only the codebook shown in FIG. 10 or11. To support this approach, the original codebook with antennaselection codewords will be optimized using 3 bits, and the PMIindicator for both the downlink and uplink signaling needs 3-bits toallow the proper selection of the increased number of codewords. Theselection of the codebook subset for this configuration can also beconfigured using the Radio Resource Configuration (RRC) signaling, whichcan select the use of codebooks in FIG. 10 or 11 instead of otherdefault codebook subsets set by the system. The attachment point mayalso select the codebook subset for the user equipment based on someknowledge of the user equipment's channel condition. The channelcondition information includes information regarding the userequipment's location information, the error rate for transmissions tothe user equipment, the number of re-transmissions to the userequipment, and the uplink sounding or other uplink transmissions, withthe uplink received beam-forming using a similar beam pattern as thatfor the downlink transmission.

The application of the signal strength weightings can also be optimizedusing an antenna beam indicator. The indicator may be a field in theuplink or downlink transmission packets. The length (number of bits) forsuch an indicator will depend on the number of available antennas in thenetwork location. One bit length is sufficient for two antennaarchitectures, while 2 bits is sufficient to designate up to fourantennas. The antenna beam indicator can also be designated according toa bit map with each bit identifying one of the available beams that canbe used to communicate with the user equipment.

Based on the specific beam location, the user equipment will provide anindicator bit value or bit map value indicating which beam can providethe best coverage for that user equipment. The use of that antenna beamindicator over a specific period of time will depend on the userequipment mobility, with the indicator being valid longer for slowermoving user equipment and being valid for a shorter period of time forfaster moving user equipment. Thus, the antenna beam indication needs tobe updated with a periodicity corresponding to the changes.

The use of an antenna beam indicator is made possible through theestimation of the uplink transmission condition, such as an analysis ofthe sounding, random access, or other types of uplink transmissions fromthe user equipment. The access point may also use a direction-findingalgorithm to determine the beam index for user equipment using the SDMAprotocols. The CQI index can be used to provide selection information tothe access point, which can also analyze the signal-to-interference andnoise ratio and identification of the serving beam for the userequipment.

In systems with switching beams or opportunistic beams (e.g. OSTMA), theuser equipment provides a CQI index when it is within the coverage areaof a beam that has been switched (powered) on. Based on the time whenthe CQI is received by the access point, the beam index can beimplicitly determined because the beam pattern is known by the accesspoint.

The technology as described above allows the configuration of additionalcodebooks for UE feedback in closed-loop operations, so that a moreappropriate codebook can be used to support different antennaconfigurations, e.g. correlated, uncorrelated or cross-polarized antennasystems. To allow the support of various antenna configurations thatwould be favorable for different deployment scenarios, e.g., correlated,uncorrelated or cross-polarized antenna systems, LTE-Advanced maysupport additional codebooks to be used for UE feedback in closed-loopoperations. For backward compatibility, higher-layer (RRC) signaling canbe used to configure the use of a different codebook by some or all ofthe UEs conveniently, depending on the UE capability, e.g., Rel-8 UEs orLTE-A UEs, and the deployment configuration, e.g., correlated,uncorrelated or cross-polarized antenna systems. As the codebook isconfigurable, the larger UE-specific codebook can be configured when ahigher capacity is required in the deployed system. Otherwise, thesmaller codebook can be used to minimize UE complexity.

While the foregoing has been with reference to a particular embodimentof the invention, it will be appreciated by those skilled in the artthat changes in this embodiment may be made without departing from theprinciples and spirit of the invention, the scope of which is defined bythe appended claims.

What is claimed is:
 1. A method for operating a first communicationstation to facilitate communication between the first communicationstation and a remote communication station, wherein the firstcommunication station includes a plurality of transmit antennas, themethod comprising: determining a configuration of a plurality ofcodebook subsets of a codebook, wherein each codebook subset of theplurality of codebook subsets includes a set of codebook weightingmatrices, and wherein the codebook weighting matrices define abeam-forming pattern for downlink transmissions; acquiring channelcondition information about a channel condition between the firstcommunication station and the remote communication station, wherein thechannel condition information includes information regarding uplinktransmissions that are received using a receive beam-forming patternrelated to the beam-forming pattern for downlink transmissions;selecting, based on the channel condition information, a codebook subsetfrom the plurality of codebook subsets of the codebook; selecting, fromthe selected codebook subset, an appropriate codebook weighting matrixfor the remote communication station; applying the selected codebookweighting matrix to one or more layer signals to obtain transmit signalsfor the plurality of transmit antennas; and transmitting the transmitsignals through the plurality of transmit antennas.
 2. The method ofclaim 1, wherein the channel condition information for the remotecommunication station further includes information regarding a number ofre-transmissions and error indicators.
 3. The method of claim 1, whereinthe uplink transmissions are uplink sounding transmissions from theremote communication station.
 4. The method of claim 1, wherein theapplying includes, for each of the one or more layer signals, scalingcopies of the layer signal respectively with complex weight values ofcorresponding layer-related column of the selected codebook weightingmatrix, wherein the complex weight values correspond respectively to theplurality of transmit antennas.
 5. The method of claim 1, furthercomprising: receiving an index of a codeword in the selected codebooksubset signaled using 2 bits through the PMI feedback indicator fieldvalue; and selecting the appropriate codebook weighting matrix for theremote communication station from selected codebook subset based on theindex.
 6. The method of claim 1, further comprising: transmitting anantenna beam indicator bit map, wherein each bit identifies one of theavailable beams corresponding to a codebook weighting matrix.
 7. Themethod of claim 6, further comprising: receiving an indicator accordingto the antenna beam indicator bit map.
 8. An apparatus for communicationwith a remote communication station, the apparatus comprising: aplurality of transmit antennas; and processor circuitry communicativelycoupled to the plurality of transmit antennas, the processor circuitryconfigured to: determine a configuration of a plurality of codebooksubsets of a codebook, wherein each codebook subset of the plurality ofcodebook subsets includes a set of codebook weighting matrices, andwherein the codebook weighting matrices define a beam-forming patternfor downlink transmissions; acquire channel condition information abouta channel condition between the apparatus and the remote communicationstation, wherein the channel condition information includes informationregarding uplink transmissions that are received using a receivebeam-forming pattern related to the beam-forming pattern for downlinktransmissions; select, based on the channel condition information, acodebook subset from the plurality of codebook subsets of the codebook;select, from the selected codebook subset, an appropriate codebookweighting matrix for the remote communication station; apply theselected codebook weighting matrix to one or more layer signals toobtain transmit signals for the plurality of transmit antennas; andtransmit the transmit signals through the plurality of transmitantennas.
 9. The apparatus of claim 8, wherein the channel conditioninformation for the remote communication station further includesinformation regarding a number of re-transmissions and error indicators.10. The apparatus of claim 8, wherein the uplink transmissions areuplink sounding transmissions from the remote communication station. 11.The apparatus of claim 8, wherein, in applying the selected codebookweighting matrix, the processor circuitry is further configured to: foreach of the one or more layer signals, scale copies of the layer signalrespectively with complex weight values of corresponding layer-relatedcolumn of the selected codebook weighting matrix, wherein the complexweight values correspond respectively to the plurality of transmitantennas.
 12. The apparatus of claim 8, wherein the processor circuitryis further configured to: receive an index of a codeword in the selectedcodebook subset signaled using 2 bits through the PMI feedback indicatorfield value; and select the appropriate codebook weighting matrix forthe remote communication station from selected codebook subset based onthe index.
 13. The apparatus of claim 8, wherein the processor circuitryis further configured to: transmit an antenna beam indicator bit map,wherein each bit identifies one of the available beams corresponding toa codebook weighting matrix.
 14. The apparatus of claim 13, wherein theprocessor circuitry is further configured to: receive an indicatoraccording to the antenna beam indicator bit map.
 15. A non-transitorycomputer-readable memory medium storing program instructions that, whenexecuted by a processor of a first communication station, cause thefirst communication station to: determine a configuration of a pluralityof codebook subsets of a codebook, wherein each codebook subset of theplurality of codebook subsets includes a set of codebook weightingmatrices, and wherein the codebook weighting matrices define abeam-forming pattern for downlink transmissions; acquire channelcondition information about a channel condition between the firstcommunication station and a remote communication station, wherein thechannel condition information includes information regarding uplinktransmissions that are received using a receive beam-forming patternrelated to the beam-forming pattern for downlink transmissions; select,based on the channel condition information, a codebook subset from theplurality of codebook subsets of the codebook; select, from the selectedcodebook subset, an appropriate codebook weighting matrix for the remotecommunication station; apply the selected codebook weighting matrix toone or more layer signals to obtain transmit signals for a plurality oftransmit antennas of the first communication station; and transmit thetransmit signals through the plurality of transmit antennas.
 16. Thenon-transitory computer-readable memory medium of claim 15, wherein thechannel condition information for the remote communication stationfurther includes information regarding a number of re-transmissions anderror indicators.
 17. The non-transitory computer-readable memory mediumof claim 15, wherein the uplink transmissions are uplink soundingtransmissions from the remote communication station.
 18. Thenon-transitory computer-readable memory medium of claim 15, wherein theprogram instructions further cause the first communication station to:receive an index of a codeword in the selected codebook subset signaledusing 2 bits through the PMI feedback indicator field value; and selectthe appropriate codebook weighting matrix for the remote communicationstation from selected codebook subset based on the index.
 19. Thenon-transitory computer-readable memory medium of claim 15, wherein theprogram instructions further cause the first communication station to:transmit an antenna beam indicator bit map, wherein each bit identifiesone of the available beams corresponding to a codebook weighting matrix.20. The non-transitory computer-readable memory medium of claim 19,wherein the program instructions further cause the first communicationstation to: receive an indicator according to the antenna beam indicatorbit map.